Borehole apparatus



4 Sheets-Sheet l C P LANMON ll, ETAL BOREHOLE APPARATUS Oct. 30, 1962Filed March 10, 1959 ATTORNEY 0 EM m 2 ms ME. n 5 5 Oct. 30, 1962 c PLANMON 1:, ET AL 3,060,588

BOREHOLE APPARATUS Filed March 10, 1959 4 Sheets-Sheet 4 C P Aawn/77,0)? Z7 flea/7 f-T Jaurenman v INVENTORJ wan A 7'7'ORNE Y UnitedStates Patent 3,060,588 BOREHULE APPARATUS C P Lanmon II, Friendswood,and Dean F. Saurenman,

Houston, Tex., assignors to Schlumberger Well Surveying Corporation,Houston, Tex., a corporation of Texas Filed Mar. 10, 1959, Ser. No.798,547 8 Claims. (tli. 33-178) This invention relates to boreholeapparatus and, more particularly, to new and improved measuringapparatus for engagement with the sidewall of a borehole.

Various borehole tools heretofore proposed have employed pad members,rigid arm members or spring type devices which project from a tool bodyinto contact with the sidewalls of a borehole during ascent and descentof the tool or which are projected into contact with the sidewalls afterthe tool is at the bottom of the borehole and ready for ascent. Suchtools generally have a relatively large diameter housing for poweractuating and retracting devices of a complex nature to operate the armsand, quite naturally, increase the possibility of a malfunction orsticking of the tool in the borehole with resultant increased wellcosts.

Other borehole tools, such as a radioactivity tool are eccentricallypositioned in the borehole and, to date, have no practical means forsimultaneously measuring the diameter of the borehole while logging.Hence, a separate logging run is required to obtain a log of theborehole diameter. Thus, a need is presented for a simple reliabledevice for contacting the sidewalls of a borehole and this need isfurther accentuated in the case of eccentrically positioned tools wherea log of the borehole diameter is desired.

Accordingly, it is an object of the present invention to provide new andimproved apparatus for measuring a borehole parameter such as itsdiameter.

Yet another object of the present invention is to provide new andimproved apparatus which aflords a simple and reliable means forobtaining an accurate and detailed log of the borehole diameter.

Another object of the present invention is to provide a new and improvedunilaterally flexible arm member for use with borehole apparatus whichmay be passed through a borehole in either direction.

Another object of the present invention is to provide a new and improvedarm member for use with borehole apparatus which may be passed through aborehole in either direction and is collapsible to the diameter of theborehole apparatus.

A still further object of the present invention is to provide a new andimproved unilaterally flexible arm member for use with boreholeapparatus which will permit re-runs of logs to be obtained withoutremoving the tool from the borehole.

Another object of the present invention is to provide a new and improvedself-contained apparatus which may be used in boreholes to measurediameter as an independent parameter and may be used in conjunction withother borehole apparatus.

Another object of the present invention is to provide an apparatus tomeasure a borehole parameter, such as diameter, which is not influencedby the angle or deviation of the borehole from vertical.

These and other objects of the present invention are attained bypivotally supporting, on the elongated body of a Well tool, aunilaterally flexible arm member which extends outwardly for engagementwith the sidewall of a borehole. The unilaterally flexible arm member isarticulated such that the arm member remains rigid or appoximatelystraight when subjected to bending forces acting in one direction butbends in response to oppositely directed forces. To obtain a measurementof borehole diameter, the arm member is biased with respect to the toolbody to swing outwardly in a wall-engaging position and to be in a rigidcondition so as to swing in response to borehole diameter variations asthe tool is moved, for example, upwardly. Upon reverse movement of thetool, the arm member may yieldingly bend to a collapsed condition.Provision is made for resiliently urging the arm member towards itsrigid condition to permit self-restoration from its collapsed condition,as when the tool is again moved in the original direction. The pivotalposition of the arm member, when in its rigid condition and inengagement with the sidewall of the borehole, aflords a measure of theborehole diameter.

The novel features of the present invention are set forth withparticularity in the appended claims. The present invention, both as toits organization and manner of operation, together with further objectsand advantages thereof, may best be understood by reference to thefollowing description taken in connection with the accompanying drawingsin which:

FIG. 1 is an elevational view of apparatus embodying the invention whenmoving down the borehole;

FIG. 1A is a cross-sectional view taken along line 1A1A of FIG 1;

FIG. 2 is an elevational view similar to FIG. 1 showing the apparatuswhen moving up the borehole;

FIGS. 3A, 3B and 3C are upper, middle and lower portions, respectively,in longitudinal cross section through a portion of the apparatus of FIG.1 with the arm member in its lower collapsed condition embodying theinvention;

FIG. 4 is a view in cross section taken along line 4-4 of FIG. 3A;

FIG. 5 is a view in cross section taken along line 5-5 of FIG. 3B;

FIG. 6 is a view in cross section taken along line 66. of FIG. 3B;

FIG. 7 is a perspective view of a segment of the arm member;

FIG. 8 is an elevational view illustrating a second embodiment of thepresent invention;

FIG. 9 is a front elevational View illustrating a third embodiment ofthe present invention; and

FIG. 10 is a view partially in section of a modification of thewall-engaging element shown in FIG. 3B.

Referring now to FIG. 1, a borehole 11 traversing earth formations 12receives a tool 13 which is shown in the condition it assumes duringdescent. Tool 13 is connected in the customary manner by an armoredcable 14 to a spooling winch (not shown) at the surface of the earthwhich serves to raise and lower the tool in the usual manner.

Tool 13 generally includes a swivel mounting head 16 and a tubularcaliper housing 17 which may be suitably interconnected at its lower endto other apparatus such as a radioactivity logging tool 18. For example,the logging tool 18 may be of the combination type aifording indicationsof both neutron and neutron-activated gamma radiation. Swivel head 16may be of conventional con.- struction to permit the cable 14 to rotaterelative to the caliper housing 17 and remainder of the tool 13 therebyeliminating any torque in the cable from being applied to the mainportion of the tool. This also permits the-tool to follow preferentialpositions along the borehole on subsequent repeat logging runs.

An arm member 20 which embodies the present invention has one endportion suitably secured at pivot point 21 within an upper portion ofthe housing 17, the remain ing end portion extending through anelongated window or opening 22 (see FIG. 1A) into contact with thesidewall of the borehole 11. Arm member 20 is also retractable into thehousing 17 to a collapsed position to facili- 3 tate passage throughsmaller diameter conduits or borehole sections.

While not shown, borehole 11 deviates from a vertical axi (as generallyall boreholes do) so that tool 13 gravitates to the lowermost portion ofthe sidewall and, to further insure contact of the tool 13 with thesidewall, a pair of longitudinally spaced, hard rubber eccenteringfingers 23 are provided in a lower portion of the tool below the armmember 20. Fingers 23 extend perpendicularly from the tool at an angleof 30 from a plane BB passing through the central axis of the tool andthe line of contact 13a of the tool with the sidewall of the borehole(see FIG. 1A). Other sets of eccentering fingers (not shown) may beprovided at variou positions on the tool body if so desired and,obviously, other types of eccentering devices, such as springs, or thelike, may be employed. As shown in FIG. 1A, arm member 20 and the lineof contact 13a effectively gauge the diameter of the borehole 11.

When the tool 13 is lowered in the borehole 11 (the direction shown byarrow A of FIG. 1), arm member 20 is flexed, being bent backwardstowards the upper end of the tool, whereas, when the tool is raisedtowards the surface of the earth on a logging run (FIG. 2, arrow B), thearm member 20 is unidirectionally rigid with only its tip in contactwith the sidewall of the borehole. Stated another way, arm member 20 hasfreedom of motion in a plane and is flexible only on one side of an axisin the plane. The construction and arrangement of the arm member 20 topermit this function will become more apparent in the explanation tofollow.

Referring now to FIGS. 3A, 3B and 3C, housing 17 is comprised of anupper tubular section 17a, an intermediate section 17b and a lowertubular section 17c which are welded or otherwise suitably connected toone another to form a unitary construction.

Upper housing section 17a has an upper fluid chamber 25 formed betweenthe inner walls of the housing section, an upper end plate member 26 anda lower end plate member 27. Similarly, lower housing section 17c (FIG.3C) has a fluid chamber 25a formed between the inner walls of thesection 17c, an upper end member 28 and a lower end member 29. Fluidchambers 25, 25a are interconnected by a fluid-tight elongatedpassageway 30 (see FIGS. 46) in the outer wall of the housing 17 andopenings 31, 32 in chambers 25, 250, respectively. Passageway 30 isformed between the walls of an elongated slot 33 and an elongated coverplate member 34 welded in the slot, the passageway permitting electricalconductors 35 to be passed through housing 17b without exposure todrilling fluid.

The lower end member 27 of the upper chamber 25 has an opening 36therein to permit a linkage system 37 to interconnect a potentiometer 38in upper chamber 25 to a first arm 39 of a bell crank member 40 (FIG.3B). To isolate chambers 25, 25a from the drilling fluid, a tubularrubber boot 41 is sealingly connected between the opening 36 and linkage37. More specifically, the lower end of boot 41 is sealingly clampedabout a connecting rod 42 of the linkage 37 by clamping means 43 and theupper end of the boot 41 is sealingly clamped to a tubular extension 44by a clamp means 45, the extension 44 being sealingly received by theopening 36 in the end member 27.

Chambers 25, 25a and the boot 41 are filled with a relativelyincompressible fluid 45 such as oil through access ports 46, 47,respectively, in housing sections 174, 170 so that the chambers arepressure balanced with respect to the hydrostatic pressure of the wellfluid thereby facilitating movement of connecting rod 42. The portion ofthe rubber boot 41 facing window 22 of housing section 17b is protectedfrom damage by a thin metal shielding plate 48 connected by pinconnections 49 (see FIG. 4) near the upper end of the boot and a pinconnection 49a 4 below the lower end of the boot (FIG. 3A), the plate 43being suitably slotted at 51 to permit free movement of the connectingrod 42.

A tubular sleeve 50 fitted within the inner walls of housing section 17aand secured thereto by a plate 60 and screw means 61 provides a suitablemounting base for the potentiometer 38 and a portion of linkage 37. P0-tentiometer 38 includes an elongated potentiometer body 51, one endthereof pivotally connected to a post 52 on the sleeve 5%) at a pinconnection 53, and a longitudinally slidable arm 54. Potentiometer 33has electrical conductors 55 connected in an electrical circuit of aconventional recorder means (not shown) at the earths surface in acustomary manner so that electrical signals are produced in the recorderin response to various longitudi' nal positions of slidable arm 54.Slidable arm 54 has its free end pivotally connected to a rigid linkmember 56 by a pin connection at 57, the link member 56 being pivotallyconnected to a post 58 on sleeve 50 by a pin connection at 59. Thevarious pin connections 53, 57 and 59 thereby permit slidable arm 54 tomove substantially parallel to the potentiometer body 51.

The linkage 37 thus far described has included the pivotal connection 57of slidable arm 54 and link 56. The end of slidable arm 54 is alsopivotally connected to the upper end of connecting rod 42 at a pinconnection 65 while the lower end of connecting rod 42 (FIG. 3B) ispivotally connected between a pair of parallel plate members 39a, 39b(FIG 5) by a pin connection 66, the plate members comprising the firstarm 39 of bell crank 40.

Bell crank 40 is pivotally mounted to the housing section 17b between apair of mounting posts 67, 68 (see FIG. 5) by a pin 68a, the posts 67,68 being fixed to the housing and abutting bell crank 40 so as toPrevent axial movement of the crank 40. A second crank arm 69 of bellcrank 40 is comprised of a pair of parallel plate members 69a, 69b (FIG.5) and is pivotally connected by a pin 70 to arm member 20 (FIG. 3B),the crank arm 69 being disposed angularly about 45 clockwise from thefirst crank arm 39. In the position shown, arm member 20 is retractedbetween the longitudinal edges 71, 72 of the window 22 (see FIG. 6), thewindow 22 extending longitudinally of the housing section 17b betweenthe lower end member 27 of housing section 17a and the upper end member28 of housing section 170. A tubular sleeve (not shown) may be receivedover the housing 17 and arm member 20 to retain the arm member 20 in theabove-described position for transportation or storage purposes.

Also, in the retracted position of arm 20, the first arm 39 of crank 40extends substantially perpendicular to a central axis through thehousing 17. Bell crank 40 has a third crank arm 73 (FIG. 3B) comprisedof a pair of parallel plate members 73a, 731; which are spaced angularlyabout 170 counterclockwise from the first crank arm 39. The crank arm 73is connected to spring means 74- through a linkage 75 which serves topivot the bell crank 40 in a counterclockwise direction thereby urgingthe free end portion of arm member 20 outwardly from housing section171) into contact with the sidewall of the borehole.

Linkage 75 includes a connector rod 76 slidably received near itsmidpoint in a bore 78 of a pivot block 79 which is pivotally mounted bya pin 80 between a pair of posts 81, 82 secured to housing section 17b(see FIG. 6). Pin 80 also extends through an elongated slot 83 inconnector rod 76 which permits relative longitudinal movement of the rodas well as a pivotal movement. The upper end of connector rod 76 ispivotally connected by a pin 84 to the third crank arm 73 while anopposite threaded end 85 receives threaded adjusting nuts 86.Compression spring 74 is disposed between the nuts 86 and pivot block79.

The arm member 20 of the present invention includes a plurality ofidentically formed link members 87 aligned in an end-to-endsubstantially straight line relationship. Pins 88 serve to pivotallyconnect the link members to one another, the link 87a at the outer endof the arm being connected to a wall-engaging member 89. Link members 87are generally channel shaped having polygonal shaped sidewalls 9t), 91at right angles to a connecting Wall 92 (see FIG. 7). End surfaces 93,94- terminate the lengthwise dimension of sidewalls 98, 91 and areadapted to cooperate, when the members 87 are interconnected to providea rigid condition for the arm member when bending forces are applied inone direction to the arm. End surface 93 is formed from one end surface92a of connecting wall 92 and portions of the adjoining end surfaces99a, 91a of sidewalls 90, 91. Adjacent to end surfaces 99a, 91a are ears95, 96 which project laterally and outwardly of end surface 93 and areseparated therefrom by relief slots 97 (see PEG. 3B). Ears 95, 96 areoifset inwardly and parallel to one another a sutlicient distance so asto be slidably received within the sidewalls of an adjacent link memberand permit abutment of end surface 93 of the one link member with endsurface 94 of the adjacent link member. Pin receiving holes 98 areprovided in ears 95, 96 and are arranged to register with piin receivingholes 99 located in sidewalls 99, 91 near the end surface 94, the axesof holes 98, 99 lying in a plane parallel to a segment 100 of connectingwall 92. Another segment 191 of connecting wall 92 is inclined outwardlyand away from the plane through the central axesof holes 98, 99 so as toform a wedge-shaped, wallengaging portion having an apex 182 at thejunction between segment 1-01 and end surface 94. End surface 93 isalsoinclined very slightly towards ears 95, 96 so that, when link members 87are pivotally connected by pins 88,arm 20 has a slight arc outwardlyaway from housing 17 (see FIG. 3B) to facilitate flexing of the arm inone direction.

A torsion spring 103 is received about each pin 88 and has end portionsin contact with connecting walls 92 of the, adjacent link members tobias end surfaces 93, 9d of adjacent link members normally intoabutment. Hence, counterclockwise bending moment applied to a pair oflink members will increase the bias of spring 103 on the members so thatwhen the bending moment is removed, the. link members will be biasedback to their original inline position.

Wall-engaging member 89 is rigidly secured to the outer link member 87aby pins 851] and 104 (FIG. 3B), the forward portion 195 or" member 89being tapered to an apex 1 06 which is adapted to slidably engage thesidewall of the formation when it is moved in one direction and todiginto the sidewall when it is moved in an opposite direction. Apex teeis arranged to lie on the arc of. the arm member 28 hence facilitatingbending of the. arm.

As described previously, arm 28 is pivotally connected at; pin,78; tocrank arm 69 and it will now be appreciated that. with this arrangement,a clockwise bending moment applied to the arm 20 about pin 70 willproduce a pivotal movement of bell crank 48 since the adjacent endsurfaces. 93,.94, of. each of the link members 88 are in abutment.thereby preventing relative movement between the link: members. On theother hand, if a counterclockwise bending moment is applied to the arm28 about pin 70, each link member will pivot freely about the respectivepivotpins 88 against the bias of the independent torsion springs 103.

Referring now to FIG. 2, if the tool is initially in the position shown,when the tool 13 is moved in a downward direction as shown by the arrowB, the apex 1126 OLWaII-engaging member 89 digs into the sidewall andpivots linkmember 8701 with respect to its adjacent link member so thatthe wall-engaging portion of link member 87 i1.digs intothe sidewall asshown in the dotted line construction. As the tool continues movement ina downwardldirection, each link member is successively pivoted and digsinto the sidewall with its wall-engaging portion until the tool is inthe position shown in FIG. 1 whereupon it may be lowered to any desireddepth in the borehole, the wall-engaging portions being dragged alongthe sidewall.

To reverse the position of the arm member 20 in an operating position,the tool 13 is moved upward as shown by the dotted arrow A whereuponeach link member is successively pivoted in a clockwise direction (shownin the dotted line construction), the wall-engaging portions of the linkmembers providing a sufficient wall-engaging force to prevent movementof the link members upwardly relative to the sidewall of the borehole.Thus, the arm member 20 again assumes a rigid position as shown in FIG.2.

With the arm 20 in a rigid position, as the tool is raised, the apex 106of the wall-engaging member 89, through the link members 87', is urgedagainst the sidewall of the borehole by the bell crank 40 and springmeans 74. As the borehole diameter varies, the apex 106 follows thevariations and, through the rigid arm member 24), pivots bell crank 40thereby producing an electrical signal in potentiometer 38 in electricallinear response to vari ations in borehole diameter. For example, at apredetermined position of the arm, the electrical response will be atone value whereas if the measured borehole diameter decreases by onehalf, the electrical response will be one half of its original value.

Referring now to FIG. 8, the invention may be embodied in an arm member20' comprised of a plurality of I tubular segments 109 pivotallyconnected to one another by pivot connections 110 at their uppermost,adjacent walls. One end of arm 20 is pivotally connected at 111 to thetool 13, the other end having a wall-engaging member 112. A coiledspring 113 received within the cylinders 109 provides the restoringforce necessary to straighten the arm 20". As will be readily apparent,this apparatus functions similarly to the above-described embodiment.

In another embodiment shown in FIG. 9, an arm member 20" is comprised ofa coiled spring 115 which is pivotally connected at one end to the tool13 at 116 and has at its other end a wall-engaging member 117. Theuppermost loops of the spring 115 are connected or secured to oneanother by suitable clamping means 118 or the like so that arm member20" has a bending characteristic. Arm 22 also functions similarly to theabovedescribed embodiment.

The wall-engaging member 89 of sensing arm 29 may also assume a form 89'as shown in FIG. 10 wherein an, electrode 120 is connected to the end ofa nonconductive member 121 and an electrical conductor 122 is passedthrough the nonconductive member and arm member 20 to appropriateelectrical measuring circuits so that the electrode may serve to measurea parameter of the borehole or to provide electrical lubrication asdescribed in Barreteau Patent No. 2,855,685.

It should also be apparent that while the foregoing embodimentsillustrate only a single arm arrangement, more than one arm can beemployed. Likewise the unilaterally flexible arm can be operated in aninverted fashion if so desired. In addition, it will be obvious, otherlinkage arrangements can be employed.

While particular embodiments of the present invention have been shownand described, it is apparent that changes and modifications may be madewithout departing from this invention in its broader aspects, andthereforethe: aim. in the appended claims is to cover all such changesand modifications as fall within the true spirit and scope ofthisinvention.

What is claimed is:

l. Borehole apparatus for use in a borehole comprising: an elongatedsupport adapted for passage through a borehole, an elongatedunilaterally flexible arm disposed in a longitudinal plane passingthrough said support, means to pivotally connect a first end portion ofsaid arm to said support, actuator means connected to said first endportion to urge the opposite end portion of said arm outwardly of saidsupport into contact with the sidewall of the borehole, said armincluding a plurality of elements arranged to lie on one side of an axisin said longitudinal plane, means to pivotally interconnect saidelements, and means on cooperating portions of said elements to preventrelative rotation between said elements relative to said axis when abending moment is applied to said arm in one direction yet permitrelative rotation between said elements through said axis when a bendingmoment is applied to said arm in an opposite direction, and means toresiliently bias said elements normally to lie on said one side of saidaxis in said longitudinal plane.

2. Borehole apparatus for use in a borehole comprising: an elongatedsupport adapted for passage through a borehole, an elongatedunilaterally flexible arm disposed in a longitudinal plane passingthrough said support, means to pivotally connect a first end portion ofsaid arm to said support, actuator means connected to said first endportion to urge the remaining end portion of said arm out wardly of saidsupport into contact with the sidewall of the borehole, said armincluding a plurality of elements arranged to align along an arcuateaxis in said longitudinal plane, means to pivotally interconnect saidelements, means on cooperating portions of said elements to preventrelative rotation between said elements when a bending moment is appliedto said arm in one direction and said elements are along said arcuateaxis yet permit relative rotation between said elements when a bendingmoment is applied to said arm in an opposite direction and means toresiliently bias said elements normally into a position along saidarcuate axis, each of said elements having individual wall-engagingprotrusions facing away from said arcuate axis.

3. In a well tool, a unilaterally flexible arm member comprised of aplurality of elements, means to pivotally connect said elements to oneanother, means on said elements to prevent relative rotation betweensaid elements in one direction when said elements are in a substantiallystraight-line alignment yet permit relative rotation in an oppositedirection, and means to resiliently bias said elements normally intosaid straight-line alignment.

4. In a well tool, a unilaterally flexible arm member comprised of aplurality of elements, means to pivotally connect said elements to oneanother, means on said elements to prevent relative rotation betweensaid elements in one direction when said elements are in a predeterminedalignment yet permit relative rotation in an opposite direction, andmeans to resiliently bias said elements normally into said predeterminedalignment.

5. Borehole apparatus for use in a borehole comprising: an elongatedsupport adapted for passage through a borehole, said support having anelongated window, an elongated unilaterally flexible arm disposed in alongitudinal plane passing through said support and adapted to bereceived in said support to have a portion thereof adapted to extendthrough said window, means to pivotally connect a first end portion ofsaid arm to said support, actuator means connected to said first endportion to urge the remaining end portion of said arm outwardly of saidsupport into contact with the sidewall of the borehole, said armincluding a plurality of elements arranged to align along an arcuateaxis in said longitudinal plane, means to pivotally interconnect saidelements, means on cooperating portions of said elements to preventrelative rotation between said elements when a bending moment is appliedto said arm in one direction and said elements are along said arcuateaxis yet permit relative rotation between said elements when a bendingmoment is applied to said arm in an opposite direction and means toresiliently bias said elements normally into a position along saidarcuate axis, each of 8 said elements having individual wall-engagingprotrusions facing away from said arcuate axis.

6. Borehole apparatus for use in a borehole comprising: an elongatedsupport adapted for passage through a borehole, an elongatedunilaterally flexible arm disposed in a longitudinal plane passingthrough said support, means to pivotally connect a first end portion ofsaid arm to said support, actuator means connected to said first endportion to urge the remaining end portion of said arm outwardly of saidsupport into contact with the sidewall of the borehole, said armincluding a plurality of elements arranged to align along an arcuateaxis in said longitudinal plane, means to pivotally interconnect saidelements, means on cooperating portions of said elements to preventrelative rotation between said elements when said elements lie alongsaid arcuate axis and said remaining end portion of said arm is notsubjected to a force along said arcuate axis yet permit relativerotation between said elements when said elements lie along said arcuateaxis and said remaining end portion of said arm is subjected to a forcealong said arcuate axis.

7. In a well tool, a housing member comprised of up per, lower andintermediate sections, said upper and lower sections having fluidchambers, said intermediate section having an elongated window, aunilaterally flexible arm member secured to said intermediate sectionhaving a portion thereof adapted to extend outwardly of said sectionthrough said window, said intermediate section having a longitudinallyextending passageway opening into said upper and lower chambers topermit electrical conductors to extend between said upper and lowersections, said chambers and passageway containing a relativelyincompressible fluid, one of said chambers having an opening adjacent tosaid intermediate section and a flexible member secured to saidintermediate section about said opening to enclose said fluid in saidchambers and said passageway whereby said chambers may be pressurebalanced with respect to pressure in said intermediate section.

8. In a well tool, a housing member comprised of upper, lower andintermediate sections, said upper and lower sections having fluidchambers, said intermediate section having an elongated window, a bellcrank pivotally mounted in said intermediate section and having firstand second arms, a unilaterally flexible arm member secured to a firstarm of said bell crank, said arm member having a portion thereof adaptedto extend outwardly of said section through said window, saidintermediate section having a longitudinally extending passagewayopening into said upper and lower chambers to permit electricalconductors to extend between said upper and lower sections, saidchambers and passageway containing a relatively incompressible fluid,one of said chambers having an opening adjacent to said intermediatesection, means for producing an electrical signal including relativelymovable members, a connecting arm member connected to one of saidrelatively movable members and to the second arm of said bell crank forproducing relative movement between said relatively movable members whensaid bell crank is pivoted, and a flexible member secured to saidintermediate section about said opening and said connecting arm memberto enclose said fluid in said chambers and said passageway whereby saidchambers may be pressure balanced with respect to pressure in saidintermediate section.

References Cited in the file of this patent UNITED STATES PATENTS 7,826Sommers Dec. 10, 1850 166,938 Richardson Aug. 24, 1875 713,784 MellorNov. 18, 1902 745,357 Lanham Dec. 1, 1903 2,534,732 Smith Dec. 19, 19502,855,685 Barreteau Oct. 14, 1958

